The present invention relates to the field of power generation, and, more particularly, to the cooling of turbine generators.
A turbine power generator generates electric power by converting mechanical energy into electrical energy. The turbine power generator typically includes a stator and rotor to generate electrical power as the rotor turns within the stator. The rotor is driven by the rotation of a drive shaft that connects to and turns the rotor. The drive shaft of the turbine power generator is, in turn, driven by steam or combustion supplied within a turbine section of the turbine power generator.
In a steam turbine generator, the shaft is driven by high-pressure saturated steam produced by a boiler and supplied to the turbine section. The boiler is fired by a fossil fuel (e.g., natural gas, coal, or lignite) or heated by a nuclear reactor. With a combustion turbine, the shaft is turned by an expansion of hot gas within the turbine section where air enters an inlet, is compressed by an air compressor, and then supplied to a combustor where fuel (e.g., natural gas) is burned to produce the hot gas. The hot gas then travels through the turbine section where the expanding gas drives the shaft of the turbine.
As the drive shaft turns the rotor within the stator, electrical current is generated and flows through respective windings mounted on the rotor and stator. The electrical current flow through the windings generates heat. Heat is also generated by hysteresis losses from changing magnetic fields, as well as from windage heating caused by moving cooling gas. Therefore, to maintain the temperature of the turbine power generator within a desirable range during its operation, a way of cooling the stator and rotor is needed. Accordingly, many large turbine generators include some type of blower and heat exchanger as well as passageways through which to circulate air or some other cooling medium (e.g., hydrogen gas). More specifically, the heat exchanger may be used as part of a cooling circuit that includes, for example, the blower for supplying the cooling medium to the heat exchanger. In some instances, particularly with respect to combustion turbine generators, a circulating cooling gas is propelled by a shaft-mounted blower and discharged to the atmosphere.
In a conventional turbine generator, the blower typically is mounted on the shaft or rotor of the electrical generator. Therefore, as the shaft is rotated, blades of the blower are rotated as well. The advantages and performance capabilities of a shaft-mounted blower, however, are limited. For example, a shaft-mounted blower has a relatively low thermal efficiency. Typically, it is 30-50 percent for a single-stage, shaft-mounted blower, as would typically be used in an air-cooled generator.
Attempts to improve the cooling of a turbine power generator have to date focused on increasing the flow of air or gas around the stator and rotor by adding additional shaft-mounted blowers in series with one another. This approach is typified by U.S. Pat. No. 5,073,087 to Harrison et al., for example, which discloses a blower hub mounted on a rotor shaft of a generator. The hub is constructed to carry four blades arranged in series with one another.
A shortcoming of this approach, however, is that blowers arranged in series with one another tend to increase flow rate at the expense of stage pressure, thereby limiting the benefit that can be obtained by adding additional pressure stages. Additional shortcomings are the cost and additional shaft length associated with multi-stage blowers.
In general, the output of a turbine generator is correlated with how well the generator can be cooled. It follows that the turbine generator""s output can be increased if the cooling capability of the blower is increased. As already noted, however, adding an additional blower in series with an existing one reduces the output of the existing shaft-mounted blower. Thus, upgrading a generator""s performance capability by using a series blower is likely to be costly because the additional series blower must be sized to compensate for the reduction in output of the existing shaft-mounted blower. Moreover, because the design and installation of new shaft-mounted blowers is difficult and costly, the opportunities provided by such blowers for upgrading the performance capability of a turbine generator are further limited.
In view of the foregoing background, it is an object of the present invention to provide a more effectively cooled turbine power generator.
This and other objects, features, and advantages in accordance with the present invention are provided by a turbine power generator having supplemental air cooling capability and related methods for generator cooling. The turbine power generator may include a housing, a shaft, a turbine for driving the shaft, a generator rotor driven by the shaft, a generator stator within the housing and surrounding the generator rotor, and a cooling gas blower for causing a main flow of gas through the housing.
More particularly, the turbine power generator preferably includes a supplemental cooling gas blower in parallel with the main cooling gas blower for causing a supplemental flow of gas through the housing to thereby more effectively cool the generator rotor and/or generator stator. Unlike conventional blowers arranged in series with one another, the main and supplemental blowers are arranged in parallel with one anther. Accordingly, the main and supplemental blowers do not generate a pressure that would otherwise offset the enhanced gas flow provided by adding the capability of the supplemental blower to that of the main blower.
The supplemental cooling gas blower may comprise an electric motor and at least one blower driven by the electric motor. Thus, whereas the main cooling gas blower may operate by rotation of a shaft-mounted set of blades, the supplemental cooling gas blower may be powered by the electric motor. The supplemental cooling gas blower may be positioned externally from the generator housing.
The main and supplemental cooling gas blowers may each include an inlet. The blower inlets may be connected in parallel with each other. The blower inlets may also be in fluid communication with at least one generator housing outlet. Additionally, the main and supplemental air blowers may each include an outlet. The blower outlets may also be connected in parallel with one another. The blower outlets, moreover, may be in fluid communication with at least one generator housing inlet.
The main and supplemental cooling gas blowers may be arranged relative to at least one of the generator rotor and the generator stator to draw gas over and through the generator rotor and/or generator stator. Alternately, the main and supplemental cooling gas blowers may be arranged relative to at least one of the generator rotor and generator stator to force a flow of cooling gas over and/or through the generator rotor and/or generator stator.
The supplemental cooling gas blower may, but need not be, used on a continual basis. Instead, the supplemental cooling gas blower may be used on a selective basis only at times when enhanced cooling capacity is needed. Accordingly, the supplemental cooling gas blower may include a controller connected, for example, to the cooling gas blower""s electric motor to allow the cooling gas blower to be operated on a selective basis.
An additional aspect of the present invention pertains to a method of cooling a turbine power generator. Cooling may be accomplished by operating the turbine power generator so that a main cooling gas blower causes a main flow of cooling gas through the housing, and additionally providing a supplemental flow of cooling gas to thereby enhance the cooling capability of the turbine power generator. The supplemental flow of cooling gas may be provided by selectively operating an electric motor of a supplemental cooling gas blower, the supplemental cooling gas blower being connected in parallel with the main cooling gas blower.